Axial piston pump



Dec. 25, 1962 D. B PURYEAR 3,070,031

AXIAL PISTON PUMP Filed Dec. 5, 1958 2 Sheets-Sheet 1 Elli-i Z0 62.56 55 31 E E 30 24 5'0 INVENTOR.

DAVID B. PURYEAR ATTORNEY.

Dec. 25, 1962 D. B. PURYEAR 3,070,031

AXIAL PISTON PUMP Filed Dec. 5, 1958 2 Sheets-Sheet 2 ANGLE o INVENTIOR.

DAVID B. PURYEAR.

ATT RNEY.

nited States atent Patented Dec. 25, 1%62 Frce The present invention relates to variable flow positive displacement fluid handling devices especially of the axial piston type, which is stable in its operation at very low flow rates; and more particularly to a variable displacement axial piston pump having improved charac teristics.

An object of the present invention is the provision of a new and improved positive displacement fluid handling device particularly of the axial piston type whose tlow rate is governed by a tiltable swash plate which will be stable, tree of cavitation, and will be more efiicient at low flow rates than have the prior art pumps of this type.

Another object of the invention is to provide a novel support structure for the tiltable swash plate wherein deflections which are generally encountered in pump operation, have minimal effect on pump operation. it is further intended that novel support structure for the swash plate of the pump be provided in such manner that the pump does not have need for heavy reinforcement structures or the like since, a greater degree of llcxibility of the swash plate is permitted without producing harmful effe Another object of the invention is to provide a supporting means for a swash plate in which the turning axis of the swash plate can be precisely located in spite of the usual manufacturing tolerances of the pump in order that pumping operation retains its controllability and eiliciency at various positions of the swash plate as it is turned on its axis to control pumping rate. This object is achieved by means of a convenient and reliable method of locating the tilting axis of the swash plate in relation to other components of the pump.

The invention resides in certain constructions and combinations and arrangements of parts; and further objects and advantages of the present invention will become apparent to those skilled in the art, to which the invention relates, from the following description of the preferred embodiment described with reference to the accompanying drawings forming a part of the specification, and in which:

Fi SURE l is a plan view of a pump embodying principles of the present invention and in which a portion is broken away to show part of its control structure;

FIGURE 2 is a cross sectional view taken upon the line 2-2 of FIGURE 1;

FIGURE 3 is a cross sectional view taken generally upon the line 33 of FIGURE 2 but in which the pumps cover plate and part of the rotor are not sectioned; and

FTGURE 4 is a view taken generally upon the line d l in FTGURE 3 to better illustrate the pumps port plate and discharge passages.

Although the invention may be otherwise embodied, it is shown and described herein as used in an axial piston pump intended to supply fluid pressure to a closed enter hydraulic system of a farm tractor and the like wherein the pump is run at very low flow rates over extended periods of time. As best seen in FIGURE 2, the pump generally comprises a housing A which provides an internal pump chamber in and is formed by a genorally cup-shaped body member 12, whose bottom forms one end wall 14 of the pump chamber it), and a removable end wall or cover plate to that is suitably bolted to the body member 12. The pump further includes an annular rotor member B that is adapted to be rotated about a longitudinally extending axis C which extends through the end walls 14 and 16,, by a shaft D. The inner end of shaft D is received in a sleeve bearing 18 mounted in the end wall 14 and the outer end of the shaft l) extends through and is suitably journalled in the removable cover plate 16. The rotor member B contains a plurality of cylinder bores Ztl (in the present instance 7) which are spaced around and extend generally parallel to the longitudinally extending axis C. The cylinder bores Kill open into the end face 22 of the rotor B which faces the end wall 14 of the pump; and each of the cylinder bores 2 is provided with a cylindrically shaped piston 24 which projects out of its receiving cylinder bore 2% toward the end wall Ibiof the pump. The rotor member i3 is suitably splined as at 26 to the shaft D so as to be rotatably driven by the shaft; and in and out movement of the pistons 24 is produced during the rotation of the rotor B by means of a swash plate E that is positioned between the end face 22 of the rotor B and the end wall 14 of the pump, and against which swash plate the projecting ends of the pistons 24 slidingly abut.

The swash plate E is nonrotatably supported in a manner which will later be described, and is adapted to be inclined at an angle with respect to the longitudinal axis C of the pump; so that as the rotor member B rotates, sliding engagement of the pistons 24- with the swash plate E causes the pistons 24 to be moved inwardly with respect to their receiving cylinder bores 20 during one-half of a revolution of the rotor member B while permitting the pistons 24 to move outwardly with respect to their cylinder bores 20 during the remaining half of each rotor rotation, to thereby produce a pumping action in each of the cylinder bores 20.

The opposite end face 28 of the rotor member B slidingly sealingly abuts a port plate F that is nonrotatably fixed to the opposite end wall 16 of the pump. The port plate F communicates the pumps suction with each of the cylinder bores 29 when their pistons 24 are moving outwardly with respect to the cylinder bores 20, and communicates each of the cylinder bores 29 with the discharge passages of the pump when the pistons 24 are moved inwardly with respect to their receiving cylinder bores 25). Assuming that the outer end of the shaft D is driven in a clockwise direction, it will be seen that the pistons move outwardly with respect to their bores 2-3 to produce a suction stroke for each of the pistons when the respective pistons are being rotated from their uppermost position, as seen in FIGURE .2, out of the plane of the drawing to their lowermost position, as seen in FIGURE 2 of the drawing. Similarly the discharge stroke for each of the pistons 24 occurs while the respective piston is being moved from the lowermost position, as seen in FIGURE 2, beneath the plane of the drawing to the uppermost position, as seen in FIG- URE 2 of the drawings. As previously indicated, the opposite end face of the rotor member B slidingly, sealingly, abuts the port plate F, and flow from each of the cylinder bores 20 is communicated to and from the opposite end face 28 of the rotor B through respective small diameter extension bores fall of the respective cylinder bores 20. The face of the port plate F to which the rotor member plate B slldingly, sealingly, abuts can best be seen in FIGURE 4 of the drawing, and for this view, the rotor rotation proceeds in a counterclockwise direction.

The suction stroke for each of the cylinder bores 2% begins when the cylinder bore extension 30 is centered upon the upper section of the vertical section line 32 as seen in FIGURE 4. in this position, the rotor ports 30 are out of register with the crescent shaped discharge port 34 and will be totally sealed off by the sealing land 36 of the port plate. The suction cycle for each rotor port proceeds as the rotor ports are moved counterclockwise, as seen in FIGURE 4, until their leading edge moves into communication with the trailing edge 33 of the port plate P, so that the rotor port will thereafter be in communication with the internal pump chamber it of the pump. The internal pump chamber lt; is C3111 tinually supplied with fluid from the pump suction connection 4%, so that outward movement of: each piston 24 during the suction stroke pulls fluid into its receiving cylinder 2t} through the rotor port 3% for substantially the remainder of the pistons outward movement. Each rotor port 3t} remains in communication with the internal pump chamber Ell during its pistons suction stroke until the trailing edge of the rotor port 3% has moved past the leading edge 42 of the port plate 5, and is thereafter sealed off by the port plates sealing land 44. This occurs at a time when its piston 24* is substantially at its most outermost limit of travel and occurs at approximately the time that the centerline of its cylinder bore it; moves into registry with the bottom portion of the vertical section line 32 as seen in FlGURE 4.

The discharge stroke for each rotor port 34) begins while the rotor port 30 is sealed oft by the port plate land 44, and continues as the centerline of its cylinder bore is being moved from the bottom portion of the vertical centerline 32 counterclockwise toward the upper portion of the vertical centerline .392 as seen in FIG- URE 4. Each rotor port 39 is sealed off during the time that it is moved a few degrees past the bottom portion of the vertical centerline 32; so that the fluid in its cylinder bore will become pressurized before being communicated to the crescent shaped discharge port 34. Inasmuch as the pump is intended to operate at presssures in the neighborhood of 2500 pounds per square inch, compressibility of the fluid is a factor; and in order to minimize the surge of pressure which occurs from the discharge port 34 into each of the cylinder bores 20 when it is first connected to the discharge port 34, a bleed groove 46 is formed in the sealing land 44 in order to throttle any surge of pressure that may occur between the discharge port 34 and the cylinder bore 20. After the leading edge of each rotor port has been moved into registry with the bleed groove 46 and the pressure has been equalized between the cylinder bore 29 and the discharge port 34, rotation toward the upper portion of the vertical centerline 32 causes fluid to be forced out of the cylinder bore 20 into the crescent shaped discharge port 34 of the port plate F. This continues until the trailing edge of each rotor port moves past the leading edge 48 of the discharge port 34, which will occur at top dead-center of its piston 24. Thereafter, each rotor port 30 will be in sealing engagement with the sealing land 36 of the port plate F for approximately 10 rotation to isolate the rotor port 39 from the suction until such time as oil in each cylinder bore is decompressed and thereafter a new rotor cycle for the cylinder bore is begun. Fluid discharge into the crescent shaped port 34 or the port plate F passes through a drilling 56 in the cover plate 16 through a vertical drilling 52-the upper end of which is counterbored and threaded to provide the discharge connection 54 of the pump.

As previously indicated, in and out motion for the respective pistons 24 is provided by abutting engagement with the angularly inclined swash plate E; and in order that the continually changing angle between each poston 24 and the surface of the swash plate E will be readily accommodated, each of the pistons 24 is provided with a slipper portion 56 having a flat cylindrically shaped head 58 which abuts the bearing surface of the swash plate E and a ball end 69 that is received within a spherical socket 62 in the main body portion of the piston.

The side edges of the spherical socket 62 engage more than one-half of the surface of the ball 6t) so as to retain the ball end at} in the socket a2; and the pistons 24 are held into slitting engagement with the swash plate E by means'of an annular retainer plate 64. The retainer plate 64 is suitably notched out around each slipper portion and bears against the back surface of its head 58 to hold each slipper in engagement with the wearing surface of the swash plate E. The annular retainer plate 64 is biased toward the swash plate E by means of an annular Washer 66 having a spherical outer surface that is received within a spherical socket 68 in the retainer plate as, and the annular washer 66 is biased toward the swash plate E by means of a coil spring 7% that is interpositioned between the annular washer 66 and the rotor member B. The coil spring 70 also serves the function of providing initial holddown force of the rotor me-1ber against the port plate F to assure sealing engagement therebetween.

As previously indicated, the pump shown in the drawing is capable of varying the quantity of its output. This, of course, is accomplished by varying the angle of the swash plate E with respect to the longitudinal axis C of the pump. Tilting of the swash plate is accomplished by means of a hydraulic piston 72 that is slidingly sealingly received in a cylinder bore 74 located above the rotor member B in the top portion of the pump. Fluid pressure supplied to the cylinder bore 7 from a control valve structure 76 causes force from the hydraulic piston 72 to be transmitted through a link 72% to move the swash plate E to its vertical or nonpurnping position wherein substantially no in and out movement of the pistons 24 is produced. The control valve 76 is intended ot regulate the discharge pressure of the pump and is adapted to maintain a preselected pressure as for example at 2500 pounds per square inch, and functions to bleed pressure fluid into the hydraulic cylinder bore 74 as the pump discharge pressure exceeds approxr-c mately 2500 p.s.i. The control valve structure 76 is formed by a bore St} which generally parallels the cylinder bore 74 and which extends through opposite end surfaces of the cup-shaped body member 12. Pressure fluid from the pump discharge 54 is conducted through a suitable drilling 82 in the removable cover plate 35 to the adjacent end or" the bore 8%. A seal is provided around the end of the bore 89 and the cover plate by means of an annular washer 84 that is positioned in a counterbore 8d. The annular washer 34 carries suitable seals which respectively engage the counterbore and cover plate, and a dish-shaped washer 33 is positioned between the bottom of the counterbore and the annular washer to bias the washer into sealing engagement with the cover plate 16. Control pressure from the control bore 30 is communicated with the cylinder bore 74 through a lateral control port drilling 9t), and the control of pressure within the drilling 96) is had by means of a spool valve 92 capable of covering the intersection of the drilling with the control bore 80. The sealing land 94 of the spool valve 92 is normally biased to a position betw n the inlet end of the control bore 8% and the control port 90 by means of a coil spring 96. Coil spring 96 i received in a counterbore 98 in the opposite end of the control bore Stl, and is interpositioned between an adjustable plug ltltl and a head N2 of th spool valve structure 92 to normally hold the head 102 in engagement with the bottom of the countcrbore 98 and the spool valve in its normal position. As the discharge pressure of the pump increases above approximately 2500 p.s.i., force upon the end of the spool valve 92 causes spring 96 to compress and permit pressure to flow into the hydraulic chamber 74 to thereby cause piston 72 to move the swash plate E into its vertical or nonpumping position. When the discharge pressure of the pump falls below approximately 2500 p.s.i., coil spring as causes the spool valve 2 to close off communication between.

control port 9%, and thereessure from the hydraulic cylinder bore 74 to th internal chamber of the pump through bore TM. The loss of pressure in cylinder bore 7 then causes the swash plate to move to an angle increasing the stroke of the pistons 24 and raising the pump pressure outlet until the pressure once again overbalances the spring at the maximum intended pressure.

Prior to the present invention, pumps with which applicant is familiar have trunnioned or journalled the swash plate E with respect to the housing A by means of cylindrical pins that have been received in cylindrical bores in the housing. Pumps so constructed were found to be quite unstable at low flow rates and to produce cavitation at these low flow rates to such a degree as to curtail their operation at low flow rates. Applicant has found that the malfunctioning of these pumps at low flow rates is produced by reason of error in the align ment of the trunnions perpendicularly with respect to the sealing surface of the port plate P so as to rotate the commutating axis of the pump oil of the vertical centerline 32 as best seen in FIGULcE 4 of the drawings. This is best shown to be true by the following mathematics with reference to FlGURES 3 and 4 of the drawings:

Let Z represent the distance between any point on the wearing surface of the swash plate and the port plate plane r ast1red in a direction perpendicular to the port plate plane and at the piston circle diameter.

Let Q represent the mean distance between the two above planes measured as above.

Let a represent the angle formed by the centerline of the trunnions with the port plate plane and represent the angle of error in positioning of the trunnions.

Let [2 represent the angle between the port late plane and the wearing surface of the swash plate on the centerline 32.

Let c represent the angle of any point in the port: plate plane measured from the top portion of the centerline 32 (the pormal commutating axis) as seen in URE 4.

Let d represent the angle-of-retard or the angle of shift of the commutating axis measured in the port plate plane from the top portion of the centerline 32.

Let R represent the radius of pumping chambers from the axis of rotation C. For the sake of simplicity assume the distances x and y, as shown in FIGURE 3, are equal. if so, then the angle a (between the wearing surface of the swash plate and port plate planes) may be measured by the error E in the placement of the adjustable ball center with respect to its proper placement. The distance between ball centers is H.

For angle b:, and for a=a small angle,

b" is zero, by superposition, (3 Z=Q+Rtanasinc-12 tanbcosc Since, for small angles of a, tan a=a,

(a) tan a= and,

RE (5) Z=Q+ sin 0-H tan b cos c The commutating axis of the pump is defined by the ction of the pistons; i.e., on one side of the axis the pistons are approaching the port plate and on the other ide receding from the port plate. Since the pistons ollow the wearing surface of the swash plate, there are two points on the surface of the port plate, one of which is closest to the swash plate and one which is furtherest away. A line between these two points is the commutating axis. Z is the distance between the wearing surface of the swash plate and the port plate. Therefore, if the point of maximum (and minimum) Z distance can be found, with respect to the angle C, the commutating axis can be located. This can be done by differentiating Equation 5 with respect to the angle c and setting the differential equation equal to zero. Thus:

aZ RE Investigation of Equation 8 in relation to the physical construction of the pump reveals that values of Equation 8 are locations of minimum Z values. Thus, for any value of b and any given error in ball location E, there is a correspondin location of the commutating axis. For small values of E and relatively large values of b, the commutating axis shift is small but the shift increases rapidly as b approaches d".

in order that the significance of Equation 8 will be more fully understood, assume that the trunnions are positioned out of a plane parallel to the port plate with an error (E as seen in FIGURE 3) of 0.610 of an inch. Likewise assume that the distance H is equal to 2.654 inches and that a pump flow capacity of 10 gals/min. occurs at an an le of b=7. With these conditions assumed the following tabulated data will be obtained from Equation 8: tan c=.603'77 cotan [1 Angle of b cotnn 1) tan c Suit; 0, degrees From the above tabulated data it will readily be seen that the commutating axis of the pump shifts out of position coincident with the plane of the centerline 32, as the swash plate approaches its nonpumping or vertical position. The significance of the shift of the com mutating axis, with respect to the suction and discharge ports of the port plate, is that a small error in positioning of the trunnions causes the pistons 2 to have suction and discharge strokes whose beginning and ending is no longer coincident with the positions for such strokes as established by the port plate P; so that the pistons 24 try to discharge fluid while they are valved off by the sealing land 36 of the port plate F, and similarly try to draw in fluid when they are valved off by the sealing land i4- of the port plate This produces instability and cavitation in the pump; and it will be seen that the severity of such cavitation and instability increases rapidly as the swash plate approaches its nonpumping position. This is clearly and vividly shown by the An le of Shift, column in the tabulated data.

In order to accurately trunnion the swash plate E with respect to the longitudinal axis C of the pump, the pump shown in the drawing employs a pair of balls G and G between the swash plate E and the end wall 14 of the pump, and about which the swash plate is adapted to be tilted. G and G will preferably be positioned on the side of the centerline C to which the control piston '72 is positioned, in order that there will always be a positive force on the swash plate which must be opposed by hydraulic pressure in its receiving cylinder bore 74. One face of each of the balls G and G is received within a. spherical socket in the swash plate E, and the other end face of the balls G and G are received in respective spherically shaped sockets that are supported from theend wall. 14 of the pump housing A. One of the balls (3 or G are made adjustable longitudinally the pump; so that after pump assembly, the centerline connecting the balls and thus the axis on which the swash plate is trunnioncd can be adjusted until it is parallel with respect to the plane or" the port plate F. In the preferred embodiment shown in the drawing, the ball G which is opposite the discharge port of the pump (and which, therefore, is subjected to the greatest pressure) is mounted in a suitable bearing block 1% that is rigidly supported by the housing member A, and ball G which is generally opposite to the suction porting provided by the port plate P is made adjustable so that its adjustment means will not be subjected to large pulsating forces. The adjustment shown in the drawing is conveniently provided by means of a threaded plug 1%, the inner end of which is spherical to receive the ball G and the outer end of which is suitably headed to accommodate shims Ill) between bottom of its head and the housing member A. By suitably adjusting the number and thickness of the shims 11% correction of the stack-up of tolerances which are inherent in the manufacture of the pump can be easily accomplished.

It has been found that fluctuation of bearing forces upon the bail G creates what is known as fretting corrosion on the ball and its swash plate receiving socket, and that this corrosion can be overcome by a passageway 112 between the wearing surface of the swash plate and the balls receiving socket. It is believed that the sliding action of the pistons slippers upon the wearing surface creates a pressure film which induces flow through the passageway 112, and thus lubricates and excludes air from the surfaces of the ball G While the invention has been described in considerable detail, I do not wish to be limited to the particular constructions shown and described; and it is my intention to cover hereby all novel adaptations, modifications and arrangements thereof which come within the practice of those skilled in the art to which the invention relates.

I claim:

1. A positive displacement variable volume pump comprising: a body member having an internal chamber therein, a rotary drive shaft received through said chamber and mounted for rotation therein, a rotor member having a 'splined connection with said drive shaft which provides the sole support for said rotor and permits axially slidable movement therein within said chamber, a swash plate positioned in said chamber between one end of said rotor member and an end wall of said internal chamber, said rotor member having a plurality of cylinder bores with the openings facing said swash plate, piston means in said cylinder bores and projecting into engagement with said swash plate. said piston means being constructed and arranged to slide around said swash plate during rotat on of said rotor member, a pair of spaced ball shaped members each disposed radially outwardly from the geometric center of said plate and separated angularly from each other by less than 180 displacement to define a trunnion support for said support plate and about which swash plate tilts to vary the stroke of said piston means, means for adiusting one of said pair of spaced ball shaped members in an axial direction, whereby adjustment of said ball angularly shifts the axis of trunnion support of said swash plate to a position parallel with a face of said rotor, and fluid pressure responsive means having fluid connections with the discharge of said pump for receiving pump pressure and movable thereby, and means operatively connected to said fluid pressure means and swash plate for effecting angular movcn it of said swash plate about its trunnion axis to we the angle of said swash plate at which pumping action is provided by said pistons.

2. A positive displacement variable volume pump comprising: a body member having an internal chamber with opposite end walls, a drive shaft rotatably supported about axis in said end walls, a rotor member including splines mounted on said drive shaft for slidable movement thereon, one end of said rotor member being in sliding and sealing engagement with one end wall of said internal chamber to provide controlled tluid flow therebetween, a swash plate positioned in said chamber about axis between said rotor member and the other end wall of said internal chamber, said rotor member having a plurality of cylinder bores with openings facing said swash plate, piston means in said cylinder bores projecting into engagement with said swash plate, said piston means being constructed and arranged to slide around said swash plate during rotation of said rotor member, a pair of spaced balls supported in the other end wall and providing a trunnion support for said swash plate about which said swash plate tilts to control the stroke of said piston means, means for adjusting one of said balls in an axial direction, high pressure port means in said one end wall of said internal chamber with which each of said cylinder openings communicate during approximately of rotation of said rotor member to maintain a positive turning force of said swash plate about its trunnion support, port means in said one end wall of said internal chamber with which each of said cylinder openings communicate during the remaining approximately 180 of rotation of said rotor means, fluid pressure sensing means having pressure communicating with the output pressure of said pump, and means operatively connected to said fluid pressure sensing means and swash plate for effecting angular movement of said swash plate about its trunnion support and operating rcsponsivcly to said fiuid pressure sensing means.

3. A positive displacement variable volume pump comprising: a body member having an internal chamber with opposite end walls defining an axis of rotation, a rotor member mounted for rotation about said axis within said chamber, a drive shaft rotatable about its longitudinal axis and having a drivable connection with said rotor member and providing longitudinal siidable movement thereon, one end of said rotor member being in sliding and sealing engagement with one end wall of said internal chamber to provide controllable fluid flow therebetween, a swash plate positioned in said chamber about said axis between the other end of said rotor member and the other end wall of said internal chamber, said rotor member having a plurality of cylinder bores with openings facing said swash plate, piston means in said cylinder bores and projecting into engagement with said swash plate, said piston means being constructed and arranged to slide around said swash plate during rotation of said rotor member, a pair of spaced convexly shaped trunnion members interpositioned between said swash plate and said other end wall of said internal chamber and about which said swash plate tilts to vary the stroke of said piston means, high pressure port means in said one end wall and with which each of said cylinder openings communicate during approximately 180 of rotation of said rotor member, port means in said one end wall with which each of said cylinder openings communicate during the remaining approximately 180 of rotation of said rotor means, at least one of said trunnions being adjustable in an axial direction, whereby adjustment thereof angularly shifts the commutating axis of said swash plate.

4. A hydro-mechanical positive displacement variable volume pump comprisin a body member having an internal chamber with opposite end walls, a drive shaft mounted for rotation about an axis in said end Walls, a rotor member carried by said shaft and driven thereby within said chamber and axially slidable thereon, one end of said rotor member being in sliding engagement with one end wall of said internal chamber to provide controlled fluid flow therebetw-een, a swash plate positioned in said chamber about said axis between the other end of said rotor member and the other end wall of said internal chamber, said rotor member having a plurality of cylinder bores with opening facing said swash plate, piston means in said cylinder bores and projecting into engagement with said swash plate, said piston means being constructed and arranged to slide around said swash plate during rotation of said rotor member, a pair of spaced convexly shaped trunnion members disposed between said swash plate and said other end wall of said internal chamber to define a trunnion support about which said swash plate tilts to vary the stroke of said piston means, means for adjusting at least one of said trunnion members in an axial direction, discharge port means in said one end wall with which each of said cylinder openings communicate during approximately 180 of the rotor cycle of said rotor member, port means in said one end wall with which each of said cylinder openings communicate during the remaining approximately 180 of rotor cycle of said rotor member, and fluid pressure responsive means responsive to outlet purr p pressure to effect turning of the swash plate about its trunnion support and define its angular position determining the effective stroke of said pistons and pumping action.

5. A positive displacement pump comprising: a body member having an internal chamber with opposite end walls a drive shaft mounted for rotation in said end walls, a rotor member carried on said shaft and driven thereby through a splined connection providing slidable movement thereon, one end of said rotor member being in sliding and sealing engagement with one end wall of said internal chamber to provide a valving action therebetween, a swash plate positioned in said chamber between said rotor member and the other end wall of said internal chamber, said rotor member having a plurality of cylinder bores having openings facing said swash plate, piston means in said cylinder openings and projecting into engagement with said swash plate, said piston means being constructed and arranged to slide around said swash plate during rotation of said rotor member, a pair of spaced ball shaped trunnion members supported on said other end wall of said internal chamber and defining a trunnion support about which said swash plate tilts to vary the stroke of said piston means, means for adjusting at least one of said trunnion members in an axial direction, discharge port means in said one: end wall with which each of said cylinder openings communicate during approximately of the rotor cycle of said rotor member, port means in said one end wall with which each of said cylinder openings communicate during the remaining approximately 180 of the rotor cycle of said rotor member, a suction port in said body member communicating a low pressure fluid supply to said internal chamber, and fluid pressure responsive means having pressure communicating connections with a fluid pressure source and operatively connected to said swash plate for effecting turning movement of said swash plate about its trunnion support to define the angular position controlling the pumping action of said pistons.

6. In a positive displacement variable volume pump, the structure comprising a rigid backing, means a swash plate, two spaced convexly curved bearing members retained by said rigid backing means and located between the backing means and swash plate and defining a trunnion axis support for said swash plate which turns angularly thereon to regulate the rate of fluid discharged from said pump, two spaced seats in said swash plate Which are complementary with said bearing members and bear thereagainst, means for moving at least one of said bearing members toward or away from said swash plate, means operatively connected to said swash plate for effecting turning thereof on its trunnion axis.

7. The structure as recited in claim 6 wherein each bearing member includes a spherically shaped element, and said means for moving at least one bearing member includes a seat for the movable spherical elements, said seat being threadedly received in said rigid backing means.

References Cited in the file of this patent UNITED STATES PATENTS 516,958 Austin Mar. 20, 1894 1,697,852 Coursen Jan. 8, 1929 2,337,821 Huber Dec. 28, 1943 2,375,322 Pierce May 8, 1945 2,430,764 Gabriel Nov. 11, 1947 2,619,041 Born Nov. 25, 1952 2,635,928 Mantle Apr. 21, 1953 2,737,899 Bonnette et a1 Mar. 13, 1956 2,769,393 Cardillo et al Nov. 6, 1956 2,896,546 Lundgren et al July 28, 1959 2,914,361 Turner Nov. 24, 1959 FOREIGN PATENTS 584,665 Germany July 13, 1930 821,687 France Aug, 30, 1937 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3370 031 December 25, 1962 David Bu Puryear It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3 line 69 for "poston" read piston column 4 line 34, for "0t" read to line 64, for "th" read the ---5 column 5, line 40, for "pormal" read normal column 8, line 37, after "communicating" insert connections column 10, line l7 for backing, means" read backing means Signed and sealed this 20th day of August 1963,

(SEAL) Attest:

ERNEST w. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

